1. Field of the Invention
This invention relates to fluid valves, and more particularly, to such fluid valves which permit fluid flow in one direction and prevent fluid flow in the opposite direction. Such a valve may be used as a replacement valve in a human heart or in artificial heart pumps.
2. Description of the Prior Art
Heart valve disease in advanced forms causes severe disability and ultimately death. The quality and length of life for patients suffering from valve disease can be remarkably improved by surgical treatment, which usually involves the total replacement of the diseased valve with a prosthetic valve.
In the two decades since the first successful implantation in a human, nearly 50 different valve types have been introduced and many have been discarded; of those remaining, two basic types are in use--those constructed of human or animal tissues (tissue valves) and those constructed of cloth, metals, carbon, and plastic components (nontissue or mechanical valves).
These devices have come in various forms of flexible unicusp, bicuspid, and tricuspid valves, ball valves and "butterfly" or flapper valves.
Significant late complications following implantation of these valves can occur and are related to valve design and materials. Present valve replacements do not permit restoration of normal pressure-flow dynamics at all levels of cardiac function. Thus, there is still no clearcut choice for the surgeon and the search for the ideal replacement heart valve is continuing.
In addition artificial heart pumps are now known which have been developed to simulate the action of the human heart. Critical components in the artificial heart pump include the fluid control valves and they must operate faultlessly for an indefinite period of time with a mechanical action that does not produce excessive blood damage (haemolysis).
Stented tissue valves, that is, supported valvular grafts which may be either xenografts (heterografts) or allografts (homografts), have been used as replacement heart valves. (See, for example, Carpentier et al., J. Thorac. Cardiovasc. Surg. 68:771 (1974); Zuhdi et al., Ann. Thorac. Surg. 17:479 (1974); Horowitz et al., J. Thorac. Cardiovasc. Surg. 767:884 (1974)). In general, such grafts have been mounted on supporting frames (stents) which provide rigid orifice rings (See Weldon et al., J. Surg. Research 6:548 (1966)). Some stents have included struts capable of flexing inwardly to a limited extent, thereby reducing stresses imposed on the grafts and decreasing possible erosion of surrounding tissues of the patient (See Sugie et at., J. Thorac. Cardiovasc. Surg. 57:455 (1969); and Hardy, Human Organ Support and Replacement, 338 et. seq.). Despite the encouraging results with prosthetic tissue heart valves and in contrast to non-tissue prosthetic valves, there is a continuing need for improvement, particularly with regard to the hydrodynamic performance and long-range durability of the tissue valves.
The art is still faced with the desirability of providing an improved stent for a tissue (xenograft or allograft) heart valve which is capable of yielding to a limited extent in response to forces which tend to alter the configuration and circumference of the orifice ring, thereby improving the long-range reliability of the valves. Accordingly, continued efforts are being made to develop more efficient, reliable and biocompatible prostheses.
The results of such continued efforts are evidenced in heart valves which are disclosed in issued U.S. patents.
U.S. Pat. No. 2,832,078 issued Apr. 29, 1958 to D. T. Williams discloses an aortic heart valve including a slotted cylindrical shell with an internal three-sac membrane to provide opening and closing ports, which seal at the centre of the cylindrical shell.
U.S. Pat. No. 3,197,788 issued Aug. 3, 1965 to F-J Segger, provides an aortic heart valve including a deformable cone-shaped cusp-supporting ring, with the cusps having smooth curved surfaces.
U.S. Pat. No. 3,548,418 issued Dec. 22, 1970 to W. W. Angell et al., provides a graft-supporting ring for grafting porcine aortic valves in which the ring is generally in the form of the residual portion of a conical shell, having three struts, the ring being completely covered and having three internal depressed valve cusps.
U.S. Pat. No. 3,570,014 issued Mar. 16, 1971 to W. D. Hancock provides a stent for aortic and mitral heart valves in which the stent includes a ring and three support arms rising therefrom, to which commissures and cusps of a heart valve are attached.
U.S. Pat. No. 3,714,671 issued Feb. 6, 1973 to W. S. Edwards et al. provides a stent for supporting a tricuspid heart valve, in which the ring comprises portions of ellipses, in which the upstanding portions are covered with fabric and which terminate in radial wings, and to which three valve cusps are sutured, the valve cusps having straight trimmed edges, and being supported without tension.
U.S. Pat. No. 3,736,598 issued June 5, 1973 to B. J. Bellhouse et al. provides and aortic valve including a ring having three legs folded to U-shaped sections to which are attached three valve cusps whose free edges meet in radial planes of abutment.
U.S. Pat. No. 3,739,402 issued June 19, 1973 to D. A. Cooley et al., provides a graft support for a bicusp valve which includes a frusto-conical ring and a pair of inverted frusto-conical segments defining struts, all provided with a fabric cover, to which are secured a pair of cusps whose upper edges lie adjacent to each other to form the valve opening.
U.S. Pat. No. 3,744,062 issued July 10, 1973 to V. Parsonnet provides a heart valve construction including a stent having three lower arcuate portions and three upstanding posts, to which a fabric sheath is secured, and from which three valve leaflets, each having an arcuate edge and a straight edge are secured, so that the straight edges provide an upper meeting closure.
U.S. Pat. No. 3,755,823 issued Sept. 4, 1973 to W. D. Hancock provides a stent for heart valves in the form of a flexible stent including a ring having three spaced-apart apexes to which a cloth sleeve is attached and to which three valve cusps are attached, so that the free edges sag towards the centre, at which point they meet at a central, slightly raised point. This valve utilizes a whole porcine aortic valve which is pretreated before mounting on the stent.
U.S. Pat. No. 3,938,197 issued Feb. 17, 1976 to S. Milo provides a heart valve including a ring to which are attached a plurality of flat valve flaps whose free edges all meet in abutting relation.
U.S. Pat. No. 3,983,581 issued Oct. 5, 1976 to W. W. Angell et al. provides a heart valve stent of a particular shape, to which a covering is attached, and from which three valve cusps are attached so that their free edges meet at three commissures, and so that their common points meet at a central depression. A whole porcine xenograft is mounted to the stent.
U.S. Pat. No. 4,035,849 issued July 19, 1977 to W. W. Angell et al. provides a heart valve stent of a particular shape, to which a covering having a bead along its perimeter is attached and from which three valve cusps are attached, so that their free edges meet at three commissures and so that their common points meet at a central depression. A whole porcine xenograft is mounted to the stent.
U.S. Pat. No. 4,084,268 issued Apr. 18, 1978 to M. I. Ionescu et al. provides a heart valve including a dish-shaped cloth-covered stent having three upright posts, to which three cusps are attached, the cusps meeting at their upper edges at a flat closed portion, and in which the knots of the stitches are covered by a pledget and cover. This valve uses pretreated bovine pericardium for its three leaflets.
U.S. Pat. No. 4,106,129 issued Aug. 15, 1978 to A. F. Carpentier et al. provides a heart valve including a deformable wire-frame stent having three inverted U-shaped commissure supports, to which are secured a cover, and from which are suspended three valve leaflets meeting along the commissures. A whole porcine xenograft is mounted to the stent.
U.S. Pat. No. 4,164,046 issued Aug. 14, 1979 to D. A. Cooley provides a mitral or tricuspid valve replacement which is based on an open ring stent.
U.S. Pat. No. 4,172,295 issued Oct. 30, 1979 to R. J. Batten provides a tricuspid heart valve dish-shaped cloth-covered stent having three upright ports to which are attached three cusps meeting at their upper edges at a flat closed portion, in which the knots of the stitches are covered by a pledget and cover, and in which securing holes are provided between the cusps.
U.S. Pat. No. 4,178,639 issued Dec. 18, 1979 to J. C. Bokros provides a heart valve having an annular valve body and a pair of pivotally secured valve leaflets.
In spite of all these prior patents, improvements are still required to provide improved valves which: provide minimal obstruction to the flow of blood; have smooth surfaces to minimize haemolysis; must not be too slow in closing, thereby permitting a substantial and undesirable reflux caused by the relatively high head pressure of the pump system; in opening and closing, there should be a minimum amount of mechanical stress and strain to the valve which would materially contribute to shortening the life of the valve; provide adequate support for attachment within the heart; minimize adverse clotting effects; should not create significant turbulence in the blood stream in both systole and diastole, which can damage blood elements; provide accuracy in the size and shape of the cusps; provide accuracy in the shape and size of the stent ring; have improved reliability by minimizing stresses in the flexing cusps tissue; incorporate flexibility and deformability in their functional operation; and improve the structural alignment of the tissue relative to the stent.